This invention relates generally to measuring apparatus and more particularly to a weighing scale.
Various scales are commercially available for providing a digital or other indication of the weight of a body placed on a weighing pan. Many of the recently developed scales make use of electronic circuitry including integrated circuits and microcomputer controls for perfecting various scale operations such as weighing, counting, altering resolution, converting units, etc. In this regard, these devices comprise electronic circuitry usually including a movable transducer and mechanical interfacing means between the electronic circuitry and the weighing pan. To that end, notwithstanding the high levels of sensitivity and accuracy associated with the electronic circuitry, the overall accuracy of the scale for small weights nonetheless depends largely upon the ability of the mechanical means to avoid introducing vibrational error into the weighing process.
With regard to the prior art, scales have tended to be one of several types. One type of scale, often referred to as a balance, is constructed so that the object being weighed on the scale's weighing pan applies a downward force to the free end of a lever arm. The lever arm is arranged to pivot about a fulcrum, so that the weight of the object on the weighing pan can readily be determined in terms of how much weight or force must be applied to the opposing end of the lever arm to exactly balance or offset the load on the weighing pan. Although these types of scales tend to be fairly accurate and are generally suitable for their intended purposes, they also tend to be somewhat slow in operation (e.g., by requiring the person operating the scale to move calibrated weights along the lever arm to achieve an exact balance) and are not easily adapted for being used in combination with electronic measuring or indicator means.
Other prior art scales, of either mechanical or electronic construction have typically included spring means and a movable arm arranged to pivot about a fulcrum, wherein the object being weighed applies a generally downward force against the free end of the arm, with the spring means serving to upwardly bias or resist any downward movement of the free end. Mechanical or electrical sensing means, responsive to the lever arm's displacement are typically used to measure and indicate the weight of the object on the weighing pan. Although these scales are also generally suitable for their intended purposes, one major drawback associated with such scales is that their weighing accuracy especially for small weights, is often adversely affected by vibration in the scale's environment, i.e., vibration transmitted through the supporting structure upon which the scale is resting, to the scale. In that regard, vibration, particularly in the up/down direction, is readily transmitted to the scale so as to cause the scale's pivot arm to initially be displaced in either an upward or downward direction, followed by gradually attenuating up/down oscillations of the arm. Although these oscillations may be small in amplitude, the amount of error introduced into the weighing process as a result thereof is often sufficiently great to produce substantial weighing inaccuracies, particularly where light weight objects are being weighed.
Moreover, other types of prior art scales which do not utilize a pivot arm, but which use spring or other means to bias a platform upward against the downward force of a load being weighed, are also subject to weighing inaccuracies attributable to vibration of the type described above.